docs: fix indentation in CephCluster on PVC example yaml
docs: fix indentation in CephCluster on PVC example yaml

Copy pasting current code block results in an YAML parsing error and
this change fixing that error by adding a space where its needed

Signed-off-by: Tarun Gupta Akirala <bcc692983986fe5dd49f9973e118b385cd1049f3@users.noreply.github.com>

rook/rook,rook/rook,rook/rook,rook/rook,rook/rook